It works fine with the width . But try to set the height to 80% you will see that it won't work : for exemple :
My master page :
<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<div style="width:60%; height:80%; overflow:auto">
<asp:contentplaceholder id="ContentPlaceHolder1" runat="server">
</asp:contentplaceholder></div>
</div>
</form>
</body>
</html>
My default.aspx :
<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="Default" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<div style="height:3000px; width:1500px; background:#FFFF00;"></div>
</asp:Content>
The horizontal scrolling is working fine, but the vertical scrolling is not.